The extended survival of conditioned neutrophils increases the neutrophil transfusion efficiency. (A-E) Conditioned guinea pig or human neutrophil transfusion in a guinea pig model of S. flexneri colonic infection. Neutropenia was produced in guinea pig by cyclophosphamide injections. S. flexneri green-fluorescent protein expressing strain (pGFP) was inoculated intrarectally (10⁹ CFUs) in conventional and neutropenic guinea pigs. When indicated, neutropenic animals were transfused 1 hour postinfection with purified guinea pig (A-C) or human (D-E) neutrophils (freshly purified, conditioned/unconditioned [20 hours]). Animals were euthanized 8 hours postinfection, and tissues were collected. (A) Confocal imaging of conventional or neutropenic guinea pig colonic mucosa infected by S. flexneri pGFP upon guinea pig neutrophil transfusion: S. flexneri pGFP (green), neutrophils (MMP-9, Red), and DNA (Dapi, blue). Bars represent 20 μm. (B-D) Living S. flexneri was counted in tissues by quantifying CFUs per gram of tissue. (C-E) MPO activity in infected tissues (U/mg) was quantified. Error bars indicate SD. ***P < .001; *P < .05; “ns” indicates P > .05 (n = 3). (F-G) Percentage of viable human neutrophils recovered in guinea pig blood circulation 8 hours posttransfusion. Human neutrophils (10⁷) were transfused in neutropenic guinea pig. Eight hours posttransfusion, circulating neutrophils were purified, and viable (PI⁻) neutrophils were counted by flow cytometry. The % CD15/PI⁻ rates were averaged from 4 animals per condition. (F) Recovery rates were calculated upon freshly purified, conditioned, or unconditioned neutrophil transfusion. (G) Recovery rates were calculated upon conditioned neutrophil untransfected or transfected (siCtrl, siPCNA, siBax) transfusion. Error bars indicate SD. ***P < .001; “ns” indicates P > .05 (n = 4).